1. Field of the Invention
The present invention relates to a method for forming patterns using as an exposure energy source, for example, a KrF excimer laser of 248.4 nm or far ultraviolet rays, wherein positive patterns are produced.
2. Statement of the Prior Art
As semiconductor devices have become highly dense and highly integrated in recent years, a wavelength used in exposure devices for minute processing, especially for photolithography is getting shorter and shorter and, research has now extended even to KrF excimer laser light (248.4 nm). However, a resist suited for this wavelength has not yet been found.
Even in the case of using, for example, MP2400 (Shipley Co., Ltd.) which is currently well known and believed to be considerably highly sensitive to KrF excimer laser light and also to have a good transmission, pattern 5a after development is seriously inferior as shown in FIG. 1 and does not appear to be usable.
A cause for such poor patterns is due to poor photoreactivity of a photosensitive material in the resist. In general, photosensitive materials of naphthoquinonediazide type which have been used for conventional resists do not show a large change in transmission to a light of about 248.4 nm. In the case of MP2400 having a layer thickness of, for example, 1.0 .mu.m, a change before and after exposure to KrF excimer laser (248.4 nm) is merely several % at 248.4 nm as shown in FIG. 2. A UV spectral curve of novolak resin having a layer thickness of 1.0 .mu.m is shown in FIG. 3; as is clearly noted from comparison with FIG. 3, the reactivity of the naphthoquinonediazide type resist is inferior in reactivity. As a result, its sensitivity and transmission are low so that good resist patterns are not obtained.
It has thus been desired to develop new resists showing better reactivity with excimer laser light of 248.4 nm.